Processes are generally known in the art for producing molten glass which comprise converting molten-glass forming ingredients and water into agglomerates, heating a vertical bed of gravitationally downwardly moving agglomerates in a chamber by direct contact with a gaseous heating medium so as to produce dry, heated, non-aggregated agglomerates and then melting said agglomerates in a glass melting furnace. Most commonly, such processes are practiced by employing a glass melting furnace which is combustion fired and by employing, as at least part of the gaseous heating medium, the flue gases emanating from such furnace and especially those flue gases which have been passed through a heat exchanger, for example, a recuperator or a regenerator. In this way, sensible heat from the flue gases, instead of being wasted, is used to dry and preheat the agglomerates and pollutants in the flue gases are at least partially recovered upon direct contact with the agglomerates and recycled into the melter. Such agglomerates may be either briquettes or pellets. Representative patents dealing with the above type processes are U.S. Pat. Nos. 4,212,613, 4,184,861, 4,248,615 and 4,248,616, all of which are hereby incorporated by reference.
Additionally, those skilled in the art readily appreciate that there is a substantial amount of scrap glass, or cullet, available for use in producing molten glass. Such cullet has an organic coating thereon and U.S. Pat. No. 4,188,228 is directed to employing such scrap glass in making pellets for use in manufacturing molten glass. That patent teaches one to remove the coating prior to employing such scrap glass in the process for forming pellets. Typically, according to that patent the organic coating is removed by burning. Thus, while this patent attempts to take advantage of the economical use of scrap glass, it, unfortunately, detrimentally affects the economy of the process by adding an additional step in the manufacturing process.
In accordance with the present invention, a glass manufacturing process is provided having improved economy by allowing for the use of scrap glass having organic coating thereon and without requiring a separate, additional step of removing such coating from the scrap glass prior to its use. That is, Applicants have surprisingly found that such cullet having an organic coating thereon may be combined with the other molten-glass forming ingredients and water to form the agglomerates, and that the organic coating can be pyrolized from the scrap glass in situ, i.e., the organic coating is thermally decarbonized during the heating of the agglomerates as they move gravitationally downwardly in a vertical bed in direct contact with a gaseous heating medium.
Thus, the present invention provides for an improvement in prior art processes of the type which comprised converting molten-glass forming ingredients and water into agglomerates, heating a vertical bed of gravitationally downwardly moving agglomerates in a chamber by direct contact with a gaseous heating medium so as to produce dry heated non-aggregated agglomerates, and melting the agglomerates in a glass melting furnace. The improvement essentially resides in employing, as a portion of the molten-glass forming ingredients, glass cullet having an organic coating thereon and pyrolizing the coating in situ during the heating step. That is, the heating step is done at a temperature and for a time sufficient to thermally decarbonize the organic coating on the glass fibers.